The present invention relates to a jaw assembly comprising a master jaw and a work clamping jaw (known as a top jaw or soft jaw) for use with a scroll chuck or the like.
A prior art jaw assembly for use with a scroll chuck comprises a master jaw slidably fitted in a guide groove (such as a T slot) extending radially in a chuck body having its bottom in meshing engagement with a scroll plate, and a work clamping jaw bolted to the master jaw so as to be movable together with the master jaw.
FIG. 7 shows one of such prior art jaw in which the relative position between a work clamping jaw 4 and a master jaw 2 in the axial direction (sliding direction of the jaw) is adjustable so as to expand the range of diameter of a workpiece which the chuck can grip. The master jaw 2 is formed with a T slot 40 extending end to end. A seating nut 3 is slidably fitted in the T slot 40. A bolt 5 is screwed through the work clamping jaw 4 into the seating nut 3. The work clamping jaw 4 is slid axially with respect to the master jaw 2 to a desired position and the bolt 5 is tightened. The jaws 2 and 4 are formed with serrations 6 and 7, respectively, to couple them together in a desired position precisely and stably.
A scroll chuck having such prior art chuck jaws tends to develop looseness between the master jaw and the guide groove formed in the chuck body owing to wear and plastic deformation which progress with use. Once such looseness appears, the master jaw, which lacks rigidity owing to the provision of the T slot, will be more vulnerable to the reaction force when chucking, so that the T slot tends to gape in the transverse direction. This will deteriorate the accuracy and stability in the gripping of the workpiece and thus the machining accuracy. Such a decrease in the machining accuracy is especially remarkable with a chuck for use in deep or high-speed machining.
Further, the T slot 40 as well as the seating nut 3 unrotatably fitted in the T slot have such complicated shapes that the machining is rather difficult. This will lead to an increase in the production cost of each jaw and thus the entire chuck.